1. Field of the Invention
The present invention generally relates to acoustic imaging. More specifically, the invention relates to systems and methods utilizing transducers that are adapted to operate with low drive voltages.
2. Description of the Related Art
A prior art two-dimensional (xe2x80x9c2-Dxe2x80x9d) ultrasound transducer typically includes a linear array of transducer elements that are capable of acquiring two-dimensional image data. For example, a 2-D transducer can include a linear array of one hundred and twenty eight (128) elements. In contrast, a three-dimensional (xe2x80x9c3Dxe2x80x9d) transducer is capable of acquiring three-dimensional image data. This is accomplished by providing the elements of such a 3-D transducer in a two-dimensional array. Such an array may include over 1,000 elements, for example.
A representative example of a portion of a conventional transducer is depicted schematically in FIG. 1. Transducer 100 of FIG. 1 includes an array of transducer elements 110 that are mounted to a backing 112. Each element 110 incorporates a piezoelectric element 114, such as a lead zirconate titanate piezoelectric element (xe2x80x9cPZTxe2x80x9d), that is adapted to generate an acoustic wave in response to an applied electric field. Such an electric field is applied to the PZT by selectively applying a voltage to electrode layers (not shown) that are formed on opposing sides of the PZT. Each element 110 also includes one or more acoustic matching layers, e.g., layers 116 and 118. Each of the acoustic matching layers exhibits an acoustic impedance that is less than the acoustic impedance of the PZT, but greater than the acoustic impedance of the body into which acoustic waves are to be propagated. This arrangement couples acoustic energy more efficiently between the element and the body.
Prior art transducers, such as transducer 100 of FIG. 1, typically operate at one-half wave resonance. That is, the PZT of each element exhibits a thickness that corresponds to one-half of a wavelength to be generated by the PZT. This thickness typically necessitates the use of high drive voltages, e.g., 170V, for achieving the desired acoustic pressures. More specifically, the PZT changes shape in response to the applied electric field, therefore, the thicker the PZT, the higher the applied voltage required to achieve the same electric field across the PZT.
Referring now to FIG. 2, operation of transducer element 110 will be described in greater detail. As shown in FIG. 2, PZT 114 produces three forward-directed waves. More specifically, PZT 114 generates a first pair of waves, i.e., a forward-directed wave 210A and a corresponding backward-directed wave 210B, at the front surface 212 of the PZT. A second pair of waves, i.e., a forward-directed wave 214A and a corresponding backward-directed wave 214B, is generated at the back surface 216 of the PZT. Waves 210A, 210B and 214A, 214B are generated when an electric field is applied to the PZT via electrodes 218 and 220. Thereafter, wave 210B yields a reflected (forward-directed) wave 222 and an absorbed wave 224. Wave 224 is absorbed by backing 112, which exhibits an acoustic impedance less than that of the PZT. Forward-directed waves 210A, 214A and 222 then interfere with each other to produce a resultant wave 226.
One of the difficulties in providing an acoustic imaging system that utilizes a 3-D transducer is associated with integrating electronic components of the transducer within the housing of the transducer. In particular, the housing of a 2-D transducer may only include 128 elements, whereas the housing of a 3-D transducer may include over 1000 elements. Thus, the increased number of elements can hinder component integration.
Operational characteristics of conventional transducer elements also can render these elements less than desirable for use in a 3-D transducer. For instance, conventional transducer elements typically operate with high drive voltages (described hereinbefore), which tend to be incompatible for use with integrated circuitry. Therefore, when using conventional transducer elements in a 3-D transducer, a desired level of component integration may not be achievable through the use of integrated circuitry. Thus, it can be appreciated that there is a need for improved systems and methods that address the aforementioned and/or other shortcomings of the prior art.
Briefly described, the present invention relates to acoustic imaging. In this regard, embodiments of the invention may be construed as acoustic imaging systems. A representative acoustic imaging system includes a transducer that incorporates a backing and an acoustic element extending from the backing. The acoustic element includes a piezoelectric element and a de-matching layer. The de-matching layer is arranged between the backing and the piezoelectric element and exhibits an acoustic impedance greater than that of the piezoelectric element. Additionally, the piezoelectric element exhibits a thickness that is less than one-half of a wavelength to be generated by the piezoelectric element.
Other embodiments of the invention can be construed as methods for acoustically imaging a body. In this regard, a representative method includes: providing a transducer having a backing and an acoustic element extending from the backing; generating acoustic waves with the acoustic element; and substantially preventing acoustic energy generated by the acoustic element from propagating into the backing of the transducer.
Other systems, methods, features, and advantages of the present invention will be or become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the present invention, and be protected by the accompanying claims.